If there's anything you need to remember about U.S. campaign finance law, it's this:

For almost every set rule, there is most likely a loophole for getting around that rule.

Keeping track of America's campaign finance laws is really difficult. Why? Because they change so much!

Take a quick scroll through this NPR timeline to get a sense of just how ridiculously fickle the process has been over the last century. It's an epic and confusing ping-pong match between advocates of spending limits and clever political strategists who find ways to get around - or flat-out challenge - those rules.

And in this corner ... the Super PAC!

The most recent, and controversial, example of doing a reverse course on once-established campaign law comes in the form of the super PAC (political action committee). Illegal as recently as the 2008 presidential election, super PACs came into legitimate existence after the Supreme Court ruled two years ago that corporate campaign contributions are indeed a form of free speech (read more about that here), and have already played a major role in the current presidential race. Essentially, they allow candidates to carry out what is best described as the "Tony Soprano strategy": keep your hands clean and let your friends in the shadows beat the crap out of your rivals for you.

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Super PACs are loosely regulated independent organizations that can accept UNLIMITED contributions directly from corporations, unions, and wealthy individuals. The groups can then use as much of that money as they want to buy political ads that support a particular candidate - usually in the form of attacks against that candidate's opponent - as long as the money is spent independently of the candidate's campaign.

Super PACs open the floodgates to what is being considered the biggest wave of unlimited corporate spending and influence ever seen in the American political system. While there are still strict contribution limits for giving directly to a candidate or a political party, the super PAC pretty much allows wealthy people and organizations - aka special interests - to get around existing spending rules so as to significantly influence the outcome of elections. Super PACs are popping up like weeds, and the big one's are almost all generously funded by a very small number of super wealthy Americans and corporations. And while the groups do have to eventually disclose who their donors are, they can delay doing so for long periods of time, often until after the election.

Everyone's doing it!

All the current Republican candidates in this election have active Super PACs working on their behalf, with intentionally vague names that bear no mention to a candidate. For instance, the biggest super PAC, which supports Mitt Romney, is simply called Restore Our Future. It's already raised more than $30 million and spent over half of that. In Iowa, before the caucus vote there, the group saturated the local airwaves with millions of dollars of attack ads aimed primarily at Newt Gingrich, the initial front runner. In the end, Gingrich came in fourth place in Iowa. Check out a selection of Restore our Future's many attack ads here (NY Times).

There are currently 318 super PACs, according to the Center for Responsive Politics. They've collectively raised close to $100 million almost half that amount already (with eight months remaining the general election!). Even President Obama, who spoke out strongly against Super PACs when they were first allowed, just announced that he's encouraging his supporters to form one and start raising money for it.

Fuzzy rules

So what's the catch? The only major stipulation is that the super PACs are not allowed to "coordinate" with the candidates or campaigns they're helping out. It's a pretty fuzzy line, though, because a candidate can still help raise money for a super PAC, as long as he doesn't tell it what to do with the money. And in almost all circumstance, super PACs are run by the same people who have spent years working for the candidate. Yet, because of the required disconnect, candidates can remain completely unaccountable when one of their Super PACs produces an attack that presents potentially false information about a rival.

Some fun interactive resources

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Where the Super PACs Spend Their Dough

Super PACs, the Animated Music Video

Super PACs Explained: Political Fundraising On Steroids